The matrix runout (also called matrix number, stamper code, dead wax, or trail-off groove) is the alphanumeric code etched or stamped into the dead-wax area around the label of a vinyl record. The matrix runout encodes the catalogue number, side designation, stamper letter, and often a cutter signature. Matrix runouts are the most reliable identifier of a specific pressing variant, as each lacquer/stamper produces a unique matrix sequence. Discogs catalogues matrix runouts for most major vinyl releases.

Matrix runout, also called the runout groove area, is the smooth band of vinyl between the last grooves of recorded audio and the central label on a vinyl record. The matrix space is used by pressing plants to inscribe identification codes that uniquely identify the master plate from which the record was pressed. These inscriptions, etched into the master and transferred to every pressing, allow collectors to determine exactly which mastering session and which pressing plant produced a given copy.

For first-pressing collectors, matrix runout codes are the definitive evidence of pressing identity. Two records with identical labels can come from completely different masters with audibly different sound and very different collector value. Reading matrix codes requires good lighting and sometimes a magnifier, and the codes vary by region and era. See our guide to identifying first-pressing vinyl for the full code-reading methodology.